Barr has led the design of sediment remediation efforts in the St. Louis River estuary for over 30 years.

Over a century ago, a grassy shoreline along the St. Louis River estuary was sculpted into peninsulas and shipping slips to support industrial expansion at the western tip of Lake Superior. Decades of industrial processing—of pig iron, tar, and manufactured gas—layered hazardous byproducts in the underwater sediment beneath. In the 1980s, the facility was designated by the Minnesota Pollution Control Agency as the St. Louis River/Interlake/Duluth Tar Superfund site (SLRIDT).

The SLRIDT story isn’t unique, even within the St. Louis River estuary—a Great Lakes Area of Concern due in part to widespread legacy contamination. Its history is retold in similar forms across North America. Every year, private industries and public entities spend hundreds of millions of dollars managing and remediating contaminated sediment in commercial waterways. The central question: What to do with it all?

Rethinking the fate of contaminated sediment

“Trucking contaminated sediment to a landfill may seem like the simplest answer, but disposing of sediment is a costly undertaking and uses up dwindling landfill space,” says Barr’s Eric Hedblom, a senior geologist and the project principal for Barr’s remediation, or cleanup, for the SLRIDT site. “Even small remediation dredging projects can mean sending hundreds of truckloads to a landfill, burning funds and fuel—particularly if the degree of contamination requires special handling or containment. Sediment managers need more efficient, resilient, and sustainable options when deciding the fate of contaminated sediment. It makes sense both economically and environmentally.”

Options multiply when we think about sediment as a resource rather than a waste. If we can find ways to apply contaminated sediment to a beneficial purpose without exposing ourselves and the environment to future harm, we unearth a world of opportunities for resource efficiency. Sediment is used in construction, infrastructure maintenance, flood control, erosion mitigation, storm-surge protection, land reclamation, and even habitat restoration. Putting contaminated sediment from remediation projects to better use can save costs, energy, and landfill space compared with disposal, and it can reduce demand for mined sediment.

Barriers to avoiding the landfill

From this angle, beneficial use of contaminated sediment might seem like an obvious choice, but it comes with its own complications. Not only do sediment managers need to find a suitable use, they must also apply sound science and engineering to ensure that it doesn’t simply move a contamination problem from one place to another. Pre-treatment or containment measures may be required to avoid future hazards to human and environmental health.

How, then, can those responsible for contaminated sediment find opportunities for beneficial use and decide whether they are a better option than disposal? There isn’t a lot of guidance out there, in part because each sediment-remediation project is unique in its regulatory environment, local demand, and nature of contamination. While many state regulatory programs reflect an understanding that contaminated sediment can and should be used as a resource, they remain conservative—often because they haven’t been exposed to the latest decision-making tools, treatment technologies, and containment methods that could expand the practice.

“To identify, evaluate, and design for beneficial use, you need creativity—the kind that arrives only by bringing project partners together with interested or affected parties ...”

In 2021, the Sediment Management Working Group (SMWG), an ad-hoc group formed for information-sharing among sediment management professionals in both industry and government, commissioned a team of international sediment experts from Barr, Windward Environmental, and Deltares to conduct a literature review and prepare a white paper on the state of beneficial use. Completed in 2022 and published on SMWG’s website this month, the white paper examines the current state of the practice in North America and Europe and includes examples of projects that applied contaminated sediment for positive impacts while reducing community and environmental exposure.

Eric was a co-author. His career of over 30 years has centered on the planning, design, and implementation of contaminated-site remediation and restoration, including two of the largest sediment remediation projects in the Great Lakes. The white paper cites SLRIDT as an example of successful beneficial use.

“There’s one thing I share with all sediment managers on these projects: to identify, evaluate, and design for beneficial use, you need creativity—the kind that arrives only by bringing project partners together with interested or affected parties, such as local residents, indigenous groups, and businesses,” Eric said. “It allows people to hear other perspectives and work toward the common goal of managing the contaminated sediment.”

Lessons from SLRIDT

The cleanup of SLRIDT was complicated from the start by its location: in the heart of a Great Lakes Area of Concern, straddling the Minnesota/Wisconsin state line, and bordering a federal navigation channel. This scenario triggered involvement by the U.S. Army Corps of Engineers, U.S. Coast Guard, U.S. Environmental Protection Agency, and regulatory agencies from both states. The agencies and responsible parties didn’t agree on the best remediation method—dredging the contaminated sediment or capping it in place—and nearby residents expressed concerns about community and estuary health. To address the needs of everyone with an interest in the project, a workshop was held in Saint Paul, Minnesota.

Setting the stage, the facilitator stated there would be “no erasers”—that everyone’s perspective would be counted. Participants included national and international sediment remediation experts and representatives of the responsible parties, local, state, and federal agencies, and the neighboring community. A wide range of expertise, experience, and perspectives made it possible to think creatively about not only how best to remediate the contaminated sediment, but also how to source and apply other sediment and materials that would be needed. The collaborative beneficial-use solutions developed at the two-day workshop were the basis of the award-winning remediation and restoration design.

Instead of dredging and disposing of 140,000 cubic yards of contaminated sediment offsite, which would have meant sending thousands of truckloads through adjacent neighborhoods, the design involved converting one of the shipping slips into a contained underwater disposal facility, capped with clean sand, that would double as the foundation of restored estuary habitat. To secure the caps against erosion, the design incorporated waste rock brought by train from mines on Minnesota’s Iron Range and riprap from nearby sources. To kickstart ecological recovery, dredged organic material from a nearby compensatory mitigation project was spread over the caps. By containing the contaminated sediment on-site and locally sourcing other needed sediment, the design saved $90 million compared with an all-dredging approach and produced 106 acres of estuary habitat. Remediation and restoration construction concluded in 2011.

Eric, project manager Guy Partch, and the rest of the SLRIDT team are 12 years into the approved 30-year monitoring program, designed to ensure that legacy contamination is no longer a threat. In their presentations at this year’s Battelle Sediments Conference later this month, Eric and Guy will look back on SLRIDT’s innovative use of contaminated sediment and happily report the monitoring results show all signs of success: contamination remains contained and the restored and created aquatic habitats, including benthic organisms and plants, are thriving.

“I’d encourage anyone embarking on a sediment remediation project to plan early for engagement,” Eric said. “In the case of SLRIDT, though bringing so many perspectives to the table was daunting, it allowed for the information and resource-sharing critical to enabling beneficial use and its acceptance by the local community.”

Learn more at the Battelle Sediments Conference

Catch Eric and Guy’s presentations at the Battelle Sediments Conference this month in Tampa, Florida:

• Beneficial Use Case Study: St. Louis River/Interlake/Duluth Tar (SLRIDT) Site Remediation, Duluth, Minnesota/Superior, Wisconsin, USA 
  Wednesday, January 29, at 8:50 a.m. in D Sessions Room (Salon F, Grand Ballroom, Tampa Marriott Water Street)

• 10 Years of Monitoring at St. Louis River/Interlake/Duluth Tar Shows Integrated Remediation/Restoration Strategy Works for Ecosystem Recovery
  Wednesday, January 29, at 4:20 p.m. in A Sessions Room (Salon A/B, Grand Ballroom, Tampa Marriott Water Street)

About the authors

Eric Hedblom, senior geologist, helps clients re-envision and restore properties impaired by legacy contamination. His 30-plus-year career has been focused on the study, remediation, and restoration of contaminated sites and the management of large, complex environmental projects, primary involving sediment-related issues. His expertise includes design, permitting, regulatory compliance, and public engagement for projects in aquatic and shoreline settings, including evaluation of potential beneficial uses of sediment and other materials. He provides technical and strategic leadership for remediation and restoration planning and implementation, long-term monitoring and maintenance (LTM&M), and Natural Resource Damage Assessment (NRDA).

Contaminated sediment remediation and habitat restoration has been a key aspect of Guy Partch’s career as a senior environmental consultant. He has managed or advised on over a dozen sediment or habitat restoration projects in the St. Louis River Area of Concern (AOC). Guy also has participated in the Duluth/Superior Harbor Technical Advisory Committee, Open Water Mitigation Subcommittee, and Dredging Subcommittee meetings to advise and guide interested parties on environmental, permitting, and construction aspects of dredging and infrastructure projects. In addition, he has served on a team of local regulators, industry representatives, and environmental activists to develop a framework for the removal of BUIs in the St. Louis River AOC.